Ferro-resonant regulators are known in this field. Providing that the feed voltage remains constant they serve to maintain a constant load current when the current demand of the load varies. This advantage is paid for by various disadvantages: excess voltage appears at the output terminals when the loop is accidentially opened causing the load impedance to become infinite; the power factor (cos .phi.) is severely degraded at low load values and at low brightnesses; and finally, efficiency is satisfactory only at full load current.
Magnetic amplifier regulators are also known. They are highly reliable even under difficult climatic conditions. However, their power factor (cos .phi.) degrades badly at low brillance. They also give rise to excess voltage at open circuit, but to a lesser extent than ferro-resonant regulators. Finally, efficiency is acceptable only for nominal current at full load.
Finally, there are sinewave regulators in which the sinewave is chopped by controlled switches such as thyristors. They have the advantage of being very simple to implement and of providing good efficiency. However, the output of the regulator must be adapted to the value of the load which may take on amplitudes of four fourths, three fourths, one half, one fourth, and one eighth, in the particular case of airport lighting. The drawback of these regulators lies in the electromagnetic interference to which they give rise which pollutes the power supply network, and also to the presence of very fast variations in current which make it difficult to design protection circuits.
The present invention seeks to to improve switching type regulators by mitigating their drawbacks.
One of the objects of the invention is thus to ensure that efficiency and power factor (cos .phi.) are subjected to substantially no degradation when going from maximum brightness to lesser brightnesses (for airport lighting), or when a load is reduced to its lowest value.
Another object of the invention is to ensure that there is no excess voltage when the load circuit is open circuit, and also to ensure that there is no excess current which could damage lamps.
The invention also seeks to provide a regulator which is independent of the exact value of the feed voltage from a power supply network.
The invention also seeks to avoid any pointless fatigue in the lamps by providing a progressive rise in current.
Finally, the invention makes it possible to avoid setting up interference due to steep edges in the current waveform by ensuring that the current waveform is as nearly sinusoidal as possible.